The 22-year cycle in the geomagnetic 27-day recurrences reflecting on the F2-layer ionization

Solar cycle variations of the amplitudes of the 27-day solar rotation period reflected in the geomagnetic activity index A_p, solar radio flux F10.7 cm and critical frequency foF2 for mid-latitude ionosonde station Moscow from the maximum of sunspot cycle 18 to the maximum of cycle 23 are examined. The analysis shows that there are distinct enhancements of the 27-day amplitudes for foF2 and A_p in the late declining phase of each solar cycle while the amplitudes for F10.7 cm decrease gradually, and the foF2 and A_p amplitude peaks are much larger for even-numbered solar cycles than for the odd ones. Additionally, we found the same even-high and odd-low pattern of foF2 for other mid-latitude ionosonde stations in Northern and Southern Hemispheres. This property suggests that there exists a 22-year cycle in the F2-layer variability coupled with the 22-year cycle in the 27-day recurrence of geomaggnetic activity.